Method of positioning an aircraft jet engine noise suppressor in a convergent jet engine nozzle

Abstract

A combination convergent jet engine aircraft nozzle (86, 142, 146) and a ventilation tube (88, 136, 144) are fixed in place and have no moving parts. Ambient air is entrained through duct inlets (96, 140, 154, 160), through the nozzle walls, through hollow struts (90, 138), the struts supporting and being connected to a hollow central tube (102, 144) or a plurality of tubes (136), to adjacent the downstream end of the nozzle to mix at takeoff with the jet forming gas exhaust. The ducts (102, 136, 144) are positioned with respect to the nozzle exhaust so that entrained ambient air flows into the gas exhaust during takeoff and so that the ambient air flow is substantially restricted or shut off during cruise flight. Ambient air inlet openings (160) are formed as a porous surface, the holes through the surface being generally in the shape of louvers (166) of which downstream end portions (174) are depressed inwardly of the outer wall surface of the nozzle to provide a minimum drag along the outer nozzle periphery during cruise flight and at takeoff. A method of positioning and fixing the outlet end of a noise suppressor within a convergent nozzle so that entrained ambient air flows into the gas exhaust during takeoff to substantially reduce the engine noise and so that ambient air is substantially restricted or is shut off entirely during cruise flight. The method in which ambient air is entrained in a noise suppressor within a convergent nozzle and is exited downstream adjacent the nozzle downstream end to mix with the gas exhaust during takeoff to suppress the engine noise, and at cruise flight substantially restricting or shutting off the ambient air through the noise suppressor by turning engine exhaust gas toward the noise suppressor axis downstream of the ambient air exit.

We claim: 
     
       1. A method of positioning an aircraft jet engine noise suppressor in a convergent jet engine nozzle, that at a nozzle pressure ratio of about 2.0 for takeoff entrains sufficient ambient air for internal ventilation to provide adequate engine noise suppression, and at a nozzle pressure ratio of about 3.0 for cruise flight ambient air is substantially reduced or shut off without the aid of moving parts, comprising: providing said nozzle, said nozzle having wall means longitudinally bounding a substantially open portion, the wall means converging toward a downstream exhaust end;   inserting and connecting vent means through said wall means and within said nozzle open portion, said vent means including duct means for carrying ambient air through the wall means, into the nozzle, and to the nozzle downstream end to mix with engine exhaust gas at takeoff;   said duct means having upstream inlet and downstream outlet ends;   fixing the inlet in the wall means to entrain ambient air during takeoff; and   fixing and positioning the outlet end of the duct means with respect to the nozzle exhaust end so that the entrained ambient air flows into the gas exhaust during takeoff to substantially reduce the engine noise and so that ambient air flow is substantially restricted or is shut off entirely during cruise flight; said duct means being of substantially decreased low drag configuration, relative to air flow therethrough and gas flow therearound, said duct means being continuously open between and at upstream and downstream ends and being fixed in shape and position.   
     
     
       2. A method according to claim 1 including: positioning the duct means downstream end at a locus of all points in the nozzle flow at which the nozzle flow equals the velocity of sound, said locus being a nozzle sonic surface or at a deformed version thereof.   
     
     
       3. A method according to claim 1 including: positioning the duct means downstream end in association with the nozzle downstream end, whereby at cruise flight a sudden expansion of nozzle gas produces a turning of the gas flow toward the axis of the duct means to close off the flow of air through the duct means.   
     
     
       4. A method according to claim 1 including: terminating the downstream end of the duct means with respect to the nozzle at a locus of all points in the nozzle flow at which the nozzle flow equals the velocity of sound, said locus being the nozzle sonic surface and intersecting all or part of the periphery of the ambient air exit of the duct means.   
     
     
       5. A method according to claim 4 in which: the periphery of the end of the duct means at which the ambient air is exited is of a shape selected from one of the group consisting of cylindrical, divergent, and convergent.   
     
     
       6. A method according to claim 5 in which: said duct means in the nozzle are a plurality of tubes, each having the location of its exit end first selected to obtain the desired air entrainment curve for the nozzle pressure ratios of between about 1.0 and 3.0, and the exit end shape then selected to more closely determine the desired entrainment rate.   
     
     
       7. A method according to claim 5 in which: the location of the exit end of the duct means is first selected to obtain the desired air entrainment curve for the nozzle pressure ratios of between about 1.0 and 3.0, and the exit end shape is then selected to more closely determine the desired entrainment rate.   
     
     
       8. A method according to claim 7 including: forming the inlet of the duct means of a porous surface to have multiple small openings, said porous surface extending along an outer wall surface of the nozzle;   forming the openings generally in the shape of louvers in which downstream end portions are depressed inwardly of the outer wall surface to provide a decrease in drag.   
     
     
       9. A method according to claim 1 including: forming the inlet of the duct means of a porous surface to have multiple small openings, said porous surface extending along an outer wall surface of the nozzle.   
     
     
       10. A method according to claim 9 including: forming the openings generally in the shape of louvers in which downstream end portions are depressed inwardly of the outer wall surface to provide a decrease in drag.